Energy Scaling Method Research Articles

Similarity-Driven Topology Optimization for Statics and Crash via Energy Scaling Method

Abstract Topology optimization (TO) is used in the initial design phase to optimize certain objective functions under given boundary conditions by finding suitable material distributions in a specified design domain. Currently available methods in the industry work very efficiently to get topologically optimized design concepts under static and dynamic load cases. However, conventional methods do not address the designer’s preferences about the final material layout in the optimized design. In practice, the final design might be required to have a certain degree of local or global structural similarity with an already present good reference design because of economic, manufacturing, and assembly limitations or the desire to re-use parts in different systems. In this article, a heuristic energy scaling method (ESM) for similarity-driven TO under static as well as dynamic loading conditions is presented and thoroughly evaluated. A 2D cantilever beam under static point load is used to show that the proposed method can be coupled with gradient-based and also heuristic, nongradient methods to get designs of varying similarity with respect to a reference design. Further testing of the proposed method for similarity-driven TO on a 2D crash test case and a large-scale 3D hood model of a car body indicates the effectiveness of the method for a wide range of problems in the industry. Finally, the application of similarity-driven TO is further extended to show that ESM also has the potential for sensitivity analysis of performance with respect to the extension of design domain.

Response Energy Behavior and Blast Damage Assessment of Unconstrained Simplified Dynamic Systems Subject to Blast Loading

Objective: Understanding the response energy behavior of components in a dynamic system subject to blast loading is critical. The objective is to find the analytical relations between the response energy of free two degree of freedom (FTDOF) systems subject to blast loading and the parameters of the loading and the system itself so that the issues with damage assessment and response energy behavior can be resolved. Methods: Energy ratio (ER) is selected to capture the response energy behavior of system components. The energy scaling method is used, which has been effective in previous study for constrained single degree-of-freedom systems. FEA simulation and given experimental results are applied in verification. Results: Maximum response ER for FTDOF systems subject to blast loading is derived. Theoretical derivation and simulation reveal that response kinetic energy carried by any single mass alone out of two lumped masses in an elastic FTDOF system can be larger than the response kinetic energy of a rigid body system formed with any one of the two lumped masses alone subject to the same blast load. Proper mass ratio and timing are critical for the result. Further observations of a perfectly plastic FTDOF system and a simplified Hanssen pendulum system (SHPS) without allowing any disintegration demonstrates that the disintegration of the Hanssen pendulum system is the main reason for Hanssen’s unexpected results. This is not only supported by the observations in Hanssen’s experiment, but also reproducible with FEA simulation, in which 13% higher kinetic energy is observed due to the disintegration. FEA analysis also reveals that dishing and impulse amplification have no significant effects, less than 1.3% and 2% variations in the response energy of the simulated SHPS, respectively. However, the impulse amplification, which can directly impact response energy, is significant for light-weight objects or low-density low-resistance materials directly facing blast loading. For damage assessment, any FTDOF system can dynamically be converted into an equivalent single degree-of-freedom system. Conclusion: The energy scaling method is effective in deriving the response ER analytically and obtaining the method of damage assessment for FTDOF systems. Maximum response ER≥1 for FTDOF systems is significant different from single degree-of-freedom systems. The disintegration of the Hanssen pendulum system is the main reason of the unexpected experimental results. Careful integration and constraint of components for systems constructed with cladding layers are extremely important. Effects of dishing and impulse amplification are ignorable on SHPS. Light-weight objects or low-density low-resistance materials directly subject to blast loading can result in unexpected error in FEA simulation. The method of damage assessment for FTDOF systems is developed.

High-energy bow tie multi-pass cells for nonlinear spectral broadening applications

Multi-pass cells (MPCs) have emerged as very attractive tools for spectral broadening and post-compression applications. We discuss pulse energy limitations of standard MPCs considering basic geometrical scaling principles and introduce a novel energy scaling method using a MPC arranged in a bow tie geometry. Employing nonlinear pulse propagation simulations, we numerically demonstrate the compression of 125 mJ, 1 ps pulses to 50 fs using a compact 2 m long setup and outline routes to extend our approach into the Joule-regime.

DCT Domain Detail Image Enhancement for More Resolved Images

This paper develops a detail image signal enhancement that makes images perceived as being clearer and more resolved and so more effective for higher resolution displays. We observe that the local variant signal enhancement makes images more vivid, and the more revealed granular signals harmonically embedded on the local variant signals make images more resolved. Based on this observation, we develop a method that not only emphasizes the local variant signals by scaling up the frequency energy in accordance with human visual perception, but also strengthens the granular signals by embedding the alpha-rooting enhanced frequency components. The proposed energy scaling method emphasizes the detail signals in texture images and rarely boosts noisy signals in plain images. In addition, to avoid the local ringing artifact, the proposed method adjusts the enhancement direction to be parallel to the underlying image signal direction. It was verified through subjective and objective quality evaluations that the developed method makes images perceived as clearer and highly resolved.

Similarity control in topology optimization under static and crash loading scenarios

Topology Optimization (TO) redistributes the material within a design space to optimize certain objective functions under given constraints. Currently available TO methods do not consider the designer's preferences about the final material layout in the optimized design. Contrarily, often an improved design similar to a reference design is required because of the economic, manufacturing or assembly restrictions. In this article, the proposed heuristic similarity control methods like the Energy Scaling Method (ESM), weak passive material method, and an intuitive method of modified design domain are compared with the formal mathematical method of Optimality Criteria (OC)-based Solid Isotropic Material with Penalization (SIMP) with a similarity constraint. Initially, the methods are coupled with Hybrid Cellular Automata (HCA) and OC-based SIMP for the TO of a cantilever beam under a static point load. The ESM is found to be the most effective and further tested for similarity-based TO with HCA in crash loading scenarios. The results show that ESM can be used to control the TO process effectively.

High efficiency ultrafast water-window harmonic generation for single-shot soft X-ray spectroscopy

Fully coherent, soft X-ray attosecond pulses are now available through high-order harmonic generation (HHG); however, the output energy is insufficient for various applications, such as attosecond-scale soft X-ray nonlinear experiments, the seeding of soft X-ray free-electron lasers, attosecond-pump-attosecond-probe spectroscopies, and single-shot imaging. In this paper, we combine a newly developed TW class mid-infrared femtosecond laser and a loose focusing geometry for HHG. A soft X-ray harmonic beam up to the water window region is demonstrated, which is more than 100 times intense compared to previous works. We achieve a high conversion efficiency, low beam divergence and a significantly reduced medium gas pressure. As the first application, we demonstrate near edge X-ray absorption fine structure experiments with clear fine absorption spectra near the K- and L-edges observed. The robust energy scaling method on HHG opens the door for demonstrating single-shot absorption spectrum and live-cell imaging with a femtosecond time resolution.

Assessment of the quality of different pocket formulas in reproducing experimental sub-barrier fusion cross sections

In the frame of a new introduced energy scaling method, the Coulomb barrier heights calculated by using thirteen different forms of the pocket formulas are systematically analyzed for sub-barrier fusion cross sections of 58 heavy-ion fusion reactions, including O, Al, Si, S, Cl, Ca and Ti projectiles. It is found that the barrier heights, which are generated by the parameterized formulas based on the Zhang 2016, Sahu 1999, Puri 2015 and Puri 1992 approaches, seem to be more suitable for description of the experimental fusion cross sections at energies below the Coulomb barrier. The present obtained results show the importance of the projectile mass and surface energy coefficients in heavy-ion fusion at sub-barrier energies. A discussion concerning the fusion Q-value rule below barrier energies is presented for some fusion systems.

Nonlinear Attosecond Metrology by Intense Isolated Attosecond Pulses

For the future progress of nonlinear attosecond science, one of the most important issues is the development of high-energy isolated attosecond pulse sources. In this paper, we review our research on the energy-scaling method for isolated attosecond pulse generation, which combines infrared two-color gating and an energy-scaling method of high-order harmonic generation. By establishing the robust energy-scaling method, the maximum pulse energy of the isolated attosecond pulse reaches 1.3 $\mu$ J/pulse in the XUV region, which is almost 100-fold higher than the values ever reported before. The pulse duration of this isolated attosecond pulse is directly measured to be 500 as by the autocorrelation method using the nonlinear interaction of N $_2$ . This nonlinear experiment clearly shows that our developed isolated attosecond pulse has enough pulse energy to make a breakthrough for nonlinear attosecond metrology as well as for attosecond-pump/attosecond-probe experiments investigating electronic processes. In addition, we further extend the high-energy harmonic continuum by using the infrared two-color gating method up to the soft-x-ray region. With the aim to temporally characterize an isolated attosecond pulse in the soft-x-ray region, we demonstrate the first observation of above-threshold ionization of He with two-photon absorption of multiple higher harmonics in the soft-x-ray region.

Contrast Sensitivity 함수를 이용한 영상화질 개선 방법

We develop the signal processing method for adaptive implementing direction of signal and the frequency sensitivity of human visual system(HVS). Existing multibnad energy scaling method makes ringing artifact because it does not consider signal direction. To solve this problem, we use block gradient for signal direction in addition to existing method. And we use the fact that frequency component of signal is more sensitive than value of signal over human eyes. we enhance the signal according to contrast sensitivity function(CSF) which is the model of frequency sensitivity of human eye. Compared that the existing analysis models only improve the efficiencies in the existing systems, the developed method can process the image signals to be more desirable and suitable to HVS.

Attosecond nonlinear optics using gigawatt-scale isolated attosecond pulses

High-energy isolated attosecond pulses required for the most intriguing nonlinear attosecond experiments as well as for attosecond-pump/attosecond-probe spectroscopy are still lacking at present. Here we propose and demonstrate a robust generation method of intense isolated attosecond pulses, which enable us to perform a nonlinear attosecond optics experiment. By combining a two-colour field synthesis and an energy-scaling method of high-order harmonic generation, the maximum pulse energy of the isolated attosecond pulse reaches as high as 1.3 μJ. The generated pulse with a duration of 500 as, as characterized by a nonlinear autocorrelation measurement, is the shortest and highest-energy pulse ever with the ability to induce nonlinear phenomena. The peak power of our tabletop light source reaches 2.6 GW, which even surpasses that of an extreme-ultraviolet free-electron laser.

An integral loop test and MARS code analysis for a DVI line break LOCA in the APR1400

The transient thermal–hydraulic phenomena of a DVI (Direct Vessel Injection) line break LOCA (Loss-of-Coolant Accident) in pressurized water reactor, APR1400, were investigated. In order to understand the phenomena during the LOCA transient, a reduced-height and reduced-pressure integral loop test facility, the SNUF (Seoul National University Facility), was constructed with scaling down the prototype. For the appropriate test conditions in the experiment with the SNUF, the energy scaling method was suggested with scaling the coolant mass inventory and the thermal power for the reduced-pressure condition. According to the conditions determined by the method, the experimental study was performed with the SNUF. The experimental results showed that the phenomenon of the downcomer seal clearing played a dominant role in the reduction of the system pressure and the recovery of the coolant level in the core. That phenomenon occurred when the steam incoming from cold legs penetrates the coolant in the upper downcomer toward the broken DVI line. The experimental results were compared with the prototype analysis to estimate the energy scaling method, so that the experiment reasonably simulated the phenomena in the prototype. For the analytical investigation, the experiment was simulated with MARS code to validate the calculation capability of the code, especially for the downcomer seal clearing, which showed good agreement with the results of experiment.

Generation of Strong Optical Field in Soft X-Ray Region by Using High-Order Harmonics

For further development of a variety of applications, one of the most important issues is the improvement of output harmonic energy and conversion efficiency. We review our work on the energy scaling of high-order harmonic generation based on phase-matching using a loosely focused beam. Our harmonic energy scaling method can be universally applied to harmonic generation in the neutral rare gas target. In addition, we demonstrate a new concept for spatial separation between the high-energy pump and harmonic beam to increase the available soft X-ray energy for the applications. This method is very simple and highly useful for not only high-order harmonic generation but also longitudinally pumped X-ray lasers. By combining the high-energy high harmonic source and new spatial separation method, we successfully demonstrate focusing of the soft X-ray beam with a peak intensity of 1/spl times/10/sup 14/ W/cm/sup 2/, which is to our knowledge the highest ever reported in the soft X-ray region.

Reconstruction of the π° kinematics from γγ decay

In this paper we discuss the quality of the π° kinematics reconstructed from the measurement of both decay photons in electromagnetic segmented calorimeter. The standard method of photon energy scaling is compared to the kinematically constrained fit procedure. The χ 2 value from a fit to a given event was a subject of quantitative confidence level analysis. We demonstrate that the kinematical fit procedure has the following advantages compared to the energy-scaling method: (i) the width of the reconstructed pion energy distribution becomes narrower by 14%, and (ii) the efficiency of π° selection for the reconstruction purposes is much higher at the same confidence level. After applying the kinematical fit method to the experimental data, the reconstructed pion energy spectrum does not violate the kinematical limit imposed by the energy conservation, in contrast to the energy-scaling method.

Numerical Study of Spin and Chiral Order in a Two-DimensionalXYSpin Glass

The two-dimensional $\mathrm{XY}$ spin glass is studied numerically by a finite size defect energy scaling method at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ in the vortex representation which allows us to compute the exact (in principle) spin and chiral domain wall energies. We confirm earlier predictions that there is no glass phase at any finite $T$. Our results strongly support the conjecture that both spin and chiral order have the same correlation length exponent ${\ensuremath{\nu}}_{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\nu}}_{c}\ensuremath{\approx}2.70$. Preliminary results in 3D are also obtained.

Numerical Study of Order in a Gauge Glass Model

The XY model with quenched random phase shifts is studied by a T=0 finite size defect energy scaling method in 2d and 3d. The defect energy is defined by a change in the boundary conditions from those compatible with the true ground state configuration for a given realization of disorder. A numerical technique, which is exact in principle, is used to evaluate this energy and to estimate the stiffness exponent $\theta$. This method gives $\theta = -0.36\pm0.013$ in 2d and $\theta = +0.31\pm 0.015$ in 3d, which are considerably larger than previous estimates, strongly suggesting that the lower critical dimension is less than three. Some arguments in favor of these new estimates are given.